by Aamer Madhani, USA TODAY

The Obama administration weighed in as rebels and Syrian President Bashar Assad's government traded accusations Tuesday that the other side has deployed chemical weapons in the ongoing civil war that has left 70,000 dead.

Meanwhile, two top GOP lawmakers, Sen. John McCain and Sen. Lindsey Graham, urged Obama on Tuesday to take military action against Assad's regime if the actions are substantiated.

The administration is "looking carefully" at allegations of chemical weapons use in Syria, Carney said.

But Carney noted that there isn't any evidence that Syrian opposition fighters have used chemical weapons. He also warned Assad not to use the reports as "pretext" to launch a chemical attack and reiterated President Obama's suggestion that use of chemical weapons would spur action by the U.S.

Syria has a huge arsenal of chemical weapons and the Obama administration has been watching for any signs that Assad might deploy them. Obama said as recently as December that the "use of chemical weapons is and would be totally unacceptable and if you make the tragic mistake of using these weapons there will be consequences and you will be held accountable."

Syria's state-run news agency reported Tuesday that rebels used chemical weapons in an attack in northern Aleppo province that killed 25 people. The Russian Foreign Ministry, which has backed Assad, also backed the assertion and called the rebel use of chemical weapons an "extremely dangerous" development, according to the Associated Press.

The Obama administration has poured tens of millions of dollars in non-military aid to Syrian rebel groups, but has resisted arming the groups.

But if it is proven that Assad's regime has deployed chemicals, McCain and Graham said Obama must reconsider that stance.

"If today's reports are substantiated, the president's red line has been crossed, and we would urge him to take immediate action to impose the consequences he has promised," McCain and Graham said in a joint statement. "That should include the provision of arms to vetted Syrian opposition groups, targeted strikes against Assad's aircraft and SCUD missile batteries on the ground, and the establishment of safe zones inside Syria to protect civilians and opposition groups."

Denis McDonough, White House chief of staff, told CNN on Tuesday evening that if it is substantiated it "is a game-changer and we'll act accordingly."